The present invention relates to control systems for controlling the air to fuel ratio in an internal combustion engine.
Internal combustion engines mix air and fuel in a prescribed ratio to facilitate combustion. Engine performance and economy is affected by the air/fuel ratio. In particular, a stoichiometric air/fuel mixture achieves optimum fuel economy. For gasoline, a stoichiometric air/fuel mixture is 14.7 parts air to 1 part fuel by weight. Air/fuel ratios richer than stoichiometric (e.g. less than 14.7:1) result in increased engine power output at the expense of fuel economy. Air to fuel ratios leaner than stoichiometric (e.g. greater than 14.7:1) can lead to engine performance problems.
Some internal combustion engines mix fuel and air in a carburetor using a spray nozzle to inject fuel droplets into an air stream passing into the engine cylinders. However, modern internal combustion engines use an electronic fuel injection system to replace the carburetor as a more accurate and reliable fuel delivery system. In an electronic fuel injection system, fuel and air are mixed in the engine intake manifold by spraying fuel droplets through a fuel injector directly into the air flow. An engine control unit (ECU) maintains the desired air to fuel ratio by controlling the amount of fuel injected by the fuel injectors. The ECU is operated either closed loop mode or open loop mode.
Some prior art electronic fuel injection systems operated only in open loop mode. In open loop mode, air and fuel are delivered to the engine in accordance with a table of target air/fuel ratios internally stored in the ECU. The stored table, also known as a fuel map, is based on engine operating conditions such as throttle position, engine RPM (speed in revolutions per minute), engine temperature, air temperature and ambient air pressure. The fuel map determines the fuel delivery profile for the engine. It is known in the art that modifying the fuel map can enhance engine performance and/or fuel economy.
However, modifying the internally stored fuel map may require replacement of memory components in ECU, unless the ECU memory is electrically re-programmable, which is not typical. It is known in the art to enhance engine performance by modifying the fuel flow signals provided by the ECU to the fuel injectors. That is, the internal fuel map of the ECU is effectively modified by externally intercepting and modifying the fuel flow control signals from the ECU to the fuel supply system. The net resulting engine fuel map is, in effect, a new fuel delivery profile for the engine.
Some electronic fuel injection control systems operate in a closed loop mode in which the air/fuel ratio is directly sensed and used in an adaptive feedback control system. To sense the air/fuel ratio, a typical fuel injection system includes a standard oxygen (O2) sensor placed in the exhaust flow of the engine. Unused (unburned) oxygen in the exhaust gasses indicates a leaner air/fuel mixture (i.e., too much oxygen for the amount of fuel). Lack of oxygen in the exhaust gases indicates a richer air/fuel mixture (i.e., not enough oxygen for the amount of fuel).
For air/fuel mixtures leaner than 14.7, the standard oxygen sensor outputs a value of about 0.2 volts indicating the presence of excess oxygen in the exhaust gasses. For air/fuel mixtures richer than 14.7 the standard oxygen sensor outputs a value of about 0.8 volts indicating oxygen depletion in the exhaust gasses. In the region around stoichiometric, the transition between 0.2 and 0.8 volts is relatively abrupt. The standard oxygen sensor is also referred to as a rich/lean sensor.
The signal output of the standard oxygen sensor is an input signal to the ECU. In closed loop mode, the signal from the standard oxygen sensor is used by the ECU to control the amount of fuel sent to the fuel injectors so as to maintain an air to fuel ratio of 14.7. Specifically, a threshold of 0.5 volts is established. When the oxygen sensor output falls below 0.5, the fuel flow to the fuel injectors is increased. When the oxygen sensor output rises above 0.5, the fuel flow to the fuel injectors is decreased. The air/fuel ratio moves above and below the stoichiometric value of 14.7 as the signal from the standard oxygen sensor to the ECU fluctuates between 0.2 and 0.8 volts.
Closed loop systems typically operate in open loop mode part of the time, where the signal from the standard oxygen sensor is not used. Open loop mode is needed when the operator demands more horsepower from the engine, such as would be needed for acceleration when passing another vehicle. In open loop mode, the ECU outputs fuel flow control signals in accordance with an internally stored fuel map, while ignoring the feedback signal from the standard oxygen sensor.
The prior art technique of adding an external product to modify the fuel flow signal from the ECU is not effective in closed loop mode. When the external add-on product attempts to adjust the fuel flow to a value other than prescribed by the ECU, the ECU (which is still involved in fuel flow management and operating in closed loop mode) quickly readjusts its output in an attempt to fluctuate about a stoichiometric mixture. In other words, the add-on product and the ECU in closed loop mode conflict with each other.
And as indicated above, the oxygen sensor output transition around stoichiometric is abrupt. Furthermore, the characteristics of a standard oxygen sensor outside of its narrow stoichiometric range of operation are unstable. Although it is possible to intercept and condition the signal from a standard oxygen sensor, it is not a reliable way to adjust the air/fuel ratio to a value other than that prescribed by the ECU responsive to the standard oxygen sensor. The abrupt transition and unstable characteristics make it difficult to use the output of the standard oxygen sensor to achieve air/fuel ratios other than the stoichiometric value of 14.7:1.
The present invention is embodied in a method and apparatus for externally modifying the operation of a closed loop electronic fuel injection control system to effectively modify the engine fuel delivery profile (effective engine fuel map) to enhance engine performance.
In accordance with a first embodiment the present invention, the operation of a closed loop electronic fuel injection control system normally used with a standard oxygen sensor, is modified using an external apparatus to effectively modify the engine fuel delivery profile. The standard oxygen sensor is replaced with a wide band oxygen sensor that is capable of sensing exhaust gas properties as a measure of the actual air/fuel ratio of the intake combustion mixture over a broad range of air/fuel ratio values. The signal from the wide band oxygen sensor is intercepted, processed in a first signal-conditioning module and coupled to the input of a first type of ECU normally used with a standard oxygen sensor. The first type of ECU is programmed to seek a stoichiometric target air/fuel ratio for each closed loop engine operating condition.
For each engine operating condition (throttle position, RPM, etc.) the first signal-conditioning module determines a new target air/fuel ratio. When the signal from the wide band oxygen sensor indicates the new target air/fuel ratio, the first signal conditioning module outputs a signal simulating the output of a standard oxygen sensor at stoichiometric air/fuel ratio to said first type of ECU normally used with a standard oxygen sensor. That is, at the new target air/fuel ratio, the first signal-conditioning module outputs a signal that moves between 0.2 and 0.8 volts, thereby simulating the output of a standard oxygen sensor, so that it appears to the first type of ECU as a standard oxygen sensor operating at a stoichiometric air/fuel ratio.
In such manner, a new engine fuel delivery profile is provided by the first signal-conditioning module in a fuel injection control system having said first type of ECU normally used with a standard oxygen sensor.
In accordance with a second embodiment of the present invention, the operation of a closed loop electronic fuel injection control system that normally utilizes a wide band oxygen sensor in conjunction with a second type of ECU, is modified using a second signal-conditioning module to effectively modify the engine fuel delivery profile (effective engine fuel map) to enhance engine performance. The signal from the wide band oxygen sensor is intercepted and processed in said second signal-conditioning module. The output of the second signal-conditioning module is coupled to the input of said second type of ECU normally used to receive signals from a wide band oxygen sensor.
For each engine operating condition (throttle position, RPM, etc.), the second type of ECU has a programmed target air/fuel ratio in its internally stored fuel map. For each of those same engine operating conditions (throttle position, RPM, etc.), the second signal-conditioning module stores a corresponding new target air/fuel ratio. The second signal conditioning module determines when the signal from the wide band oxygen sensor represents the new target air/fuel ratio, and substitutes a signal representing the originally programmed target air/fuel ratio value as an input signal to the second type of ECU. That is, at the new target air/fuel ratio, the second signal-conditioning module outputs a current signal that simulates the output of a wide band oxygen sensor operating at the originally programmed target air/fuel ratio. Thus, the second signal-conditioning module appears to the second type of ECU as a wide band oxygen sensor operating at the originally programmed target air/fuel ratio.
In such manner, a new engine fuel delivery profile is provided by the second signal conditioning module in a fuel injection control system having said second type of ECU normally used with a wide band oxygen sensor.